The present invention relates to a method for fabricating a semiconductor device, and more particularly, to an etching method using a hard mask scheme in regions having different pattern densities.
As semiconductor devices become more highly integrated, a critical dimension (CD) of a gate is getting reduced. The reduction of the CD is required not only in a memory cell region but also in a peripheral region where driving circuits for driving cells, logical devices such as a decoder and a sense amplifier are formed.
Generally, a hard mask scheme is applied to a gate etch process for forming a gate of a semiconductor device. According to the hard mask scheme, a hard mask having a pattern substantially the same as a photoresist pattern which is used as an etch mask is formed under the photoresist pattern to compensate limitations of the photoresist pattern. Then, after removing the photoresist pattern, the hard mask is used as an etch mask for the gate etch process.
However, when etching a nitride layer for the hard mask during the gate etch process, a loading effect caused by the pattern density difference increases a final inspection critical dimension (FICD) of the peripheral region compared to the cell region. Even when the identical DICDs are applied to the cell region and the peripheral region, the loading effect increases the FICD compared to a develop inspection critical dimension (DICD) of the peripheral region.
Thus, it is required to reduce the DICD of the peripheral region as much as an etch CD bias corresponding to a variation value of the FICD. However, in this case, when a photo-exposure process is performed using a photo mask, a margin decreases. As a result, a pattern failure such as a collapse of the pattern in the peripheral region occurs. Furthermore, as a linewidth of the semiconductor device decreases, the gate FICD of the peripheral region decreases. Accordingly, it is required to reduce the DICD of the peripheral region as much as the etch CD bias. Therefore, the photolithography process margin decreases, making it difficult to form the patterns.